The class of congruence meet semidistributive varieties is not strong Maltsev

The rings of non-square matrices based on the dimension-keeping (DK-) semi-tensor product (STP) are considered, where a virtual identity is introduced to make each ring possess an identity element. Using this ring structure, four kinds of eigenvalues/eigenvectors (EEs) of hypermatrices, namely, the ordinary EE (OEE), the universal EE (UEE), the diagonal EE (DEE), and the horizontal diagonal EE (HDEE), are proposed with respect to preassigned matricizings. The Kronecker canonical form (KCF) of non-square pencils is used to calculate the OEEs; the monic decomposition algorithm (MDA) is then applied to extract the UEEs, DEEs, and HDEEs from them. Finally, the KCF of non-square pencils is further used to construct the KCF of a tensor, which reveals all the EEs of the tensor. The KCF of a tensor not only shares the main properties of the Jordan canonical form of matrices but also includes the latter as a special case. Consequently, all the EEs of a hypermatrix are straightforwardly computable via its KCF.

math.RA↗

arXiv2026

Phantom categories on 3-vertex directed DG quivers

We construct infinitely many pairwise non-derived-Morita-equivalent phantom categories $\mathcal{P}_{m}, m\in\mathbb{Z}$ from concrete directed DG quivers with 3 vertices. Moreover, there exists a fixed finite-dimensional DG algebra $C$ such that for each $m\in\mathbb{Z}$, there is a way to reassign cohomological gradings on $C$ (without changing the differential) to obtain a new DG algebra $C_{m}$ with $\mathrm{Perf}(C_{m})\cong \mathcal{P}_{m}$.

math.RA↗

arXiv2026

Toeplitz multiplication and graded factorization of determinant recurrences

Toeplitz matrices are matrices whose entries are constant along each diagonal. When only finitely many diagonals are nonzero, the determinants of successively larger matrices obey a fixed linear recurrence: each new determinant is a fixed linear combination of finitely many preceding ones. We ask whether the recurrence for a complicated band can be built from recurrences for simpler factors, and show that it can. Multiplying two finite banded Toeplitz matrices reproduces the expected product throughout the interior, with discrepancies only near two opposite corners. Shifting the factors relative to the main diagonal redistributes these boundary discrepancies, and the different shifts account exactly for the pieces from which the full determinant recurrence is assembled. For several factors, all allowed shifts are described by a finite system of linear inequalities, giving a systematic decomposition of the recurrence. This viewpoint also leads to a recursive construction that works directly with polynomial coefficients, without solving for their roots. When a factorization into bounded-degree pieces is supplied, a valid recurrence can be constructed using essentially a linear number of arithmetic operations in the number of coefficients that must be output. A five-diagonal example shows how a sixth-order recurrence is assembled from two tridiagonal Toeplitz factors together with two boundary contributions.

math.RA↗